GHOST
Do not forget. This visitation
Is but to whet thy almost blunted purpose.
But look, amazement on thy mother sits.
O, step between her and her fighting soul.
Conceit in weakest bodies strongest works.
Speak to her, Hamlet.
(3.4.126-131)
It looks like Hamlet was so busy laying into Gertrude for sleeping with Claudius that he forgot all about the ghost's orders for him to leave Gertrude "to heaven"—almost as if he's more upset by Gertrude's sexuality than his father's murder.